bug#3313: 23.0.93; Use Lisp strings for syntax descriptor examples

In the Elisp manual, node Syntax Descriptors, we say that a syntax
descriptor is a Lisp string. But the examples we give of syntax
descriptors are not written as strings, with double-quotes.
 
E.g., change `. 23' to ". 23", to indicate better that the descriptor
is a Lisp string.

In GNU Emacs 23.0.93.1 (i386-mingw-nt5.1.2600)
 of 2009-05-02 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'